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Fossil reveals the mystery behind evolution of flatfish eyes

The evolution of flatfish like halibut – fish with both eyes on one side of its head – has puzzled scientists for centuries. But now, Alaska Native News reports, scientists have a better idea that flatfish did evolve that way.

The latest issue of the Journal of Vertebrate Paleontology describes the find, discovered by Oxford University researcher Dr. Matt Friedman in a museum collection in Vienna. The fossil had gone unnoticed as a specimen, and Freidman noted in a press release, “It just goes to show that…not all new discoveries take place in the field.”

The fossil comes from Bolca in northern Italy and was found in marine rocks about 50 million years old. The site has been mined for fish fossils for hundreds of years, and hosts an early coral reef assemblage.

The primitive flatfish, named Heteronectes (meaning “different swimmer”), has a flattened form, but its eye had not yet migrated to the other side of its skull. The press release calls it “the perfect intermediate” between the anatomy of most fish and the flatfish.

The odd anatomy of the flatfish has been an evolutionary mystery. Early skeptics of Darwin used the fish as an argument against his theory of evolution – how could it have been advantageous for the fish to slowly evolve where both eyes are on one side of their head? The discovered fossil demonstrates that as strange as its evolution may seem, it did indeed occur.